Most communities in the U.S. prepare for floods that have a 1 percent chance of occurring in any year. Misleadingly called the "100-year flood," this is the minimum level of protection recommended by the Federal Emergency Management Agency (FEMA). While a 1 percent chance sounds small, there have been dozens of much larger floods around the country in recent years, some with odds smaller than 1-in-500 or even 1-in-1,000. The list includes South Carolina in 2015; West Virginia in 2016; Ellicott City, Md., in 2016; Louisiana in 2015 and 2016; and Texas in 2015 and 2016. While the odds of these larger floods are undoubtedly quite small, the nation sees several each year, and they have catastrophic consequences for the communities they strike.